The convergence correction in conventional cathode ray tube (which is called hereinafter a CRT) apparatus have obtained the desired convergence correcting magnetic field by flowing respectively the horizontal or vertical convergence coil with a current proportional to a parabolic waveform obtained by integrating the horizontal deflecting current or the vertical deflecting current with respect to time respectively. In such apparatus uniform convergence correction is only effected over the entire picture surface, and there have been the disadvantages that it is very difficult to effect the correction with a high accuracy over the entire picture surface and so on.